The field of art has known a number of different jaw designs. For example, the 29 Apr. 1980 saw the issuance of U.S. Pat. No. 4,200,300, which discloses the idea of utilizing removable jaws. Twelve years later, U.S. Pat. No. 5,141,239 was issued on Aug. 25, 1992. This patent illustrates a jaw designed to grip a workpiece internally or externally within the extendable range of a scroll chuck. In 1995, this patent was improved upon by U.S. Pat. No. 5,464,231, in which curved engagement surfaces were added on the jaws. Although an improvement, the described jaws provide a maximum clamping surface contact area between the jaws and the workpiece when the chuck is positioned at its minimum diameter clamping range. As the chuck's clamping diameter is expanded, the surface contact area between the jaws and the workpiece actually decreases; thus, reducing the gripping force of the jaws on the workpiece as the workpiece diameter increases. Given a fixed rotation velocity, centrifugal forces on the surface of a rotating workpiece are greater on workpieces of larger diameter versus those of smaller diameter, yet the prior art described above reduces its gripping force as the workpiece diameter increases. What is needed is a jaw assembly that improves the gripping force on the workpiece as the chuck's clamping diameter is increased.
Additionally, the prior art contains jaws that are designed to function best as inner gripping expansion jaws, and others that work best as outer gripping compression jaws. It is difficult to perform both tasks well. Yet another limitation of current jaw designs is that they unduly limit the minimum and maximum diameter range of a given lathe chuck. What is needed is a jaw assembly that provides improved gripping forces for both expansion and compression arrangements while increasing the minimum to maximum diameter range of a chuck.